RESUMEN
The sustained increase in the incidence of nontuberculous mycobacterial (NTM) infection and the difficulty in distinguishing these infections from tuberculosis constitute an urgent need for NTM species-level identification. The MeltPro Myco assay is the first diagnostic system that identifies 19 clinically relevant mycobacteria in a single reaction based on multicolor melting curve analysis run on a real-time PCR platform. The assay was comprehensively evaluated regarding its analytical and clinical performances. The MeltPro Myco assay accurately identified 51 reference mycobacterial strains to the species/genus level and showed no cross-reactivity with 16 nonmycobacterial strains. The limit of detection was 300 bacilli/ml, and 1% of the minor species was detected in the case of mixed infections. Clinical studies using 1,163 isolates collected from five geographically distinct health care units showed that the MeltPro Myco assay correctly identified 1,159 (99.7%) samples. Further testing with 94 smear-positive sputum samples showed that all samples were correctly identified. Additionally, the entire assay can be performed within 3 h. The results of this study confirmed the efficacy of this assay in the reliable identification of mycobacteria, suggesting that it might potentially be used as a screening tool in regions endemic for tuberculosis.
Asunto(s)
Técnicas Microbiológicas/métodos , Técnicas de Diagnóstico Molecular/métodos , Infecciones por Mycobacterium no Tuberculosas/diagnóstico , Micobacterias no Tuberculosas/aislamiento & purificación , Coinfección/diagnóstico , Coinfección/microbiología , ADN Bacteriano/genética , ADN Espaciador Ribosómico/genética , Humanos , Técnicas Microbiológicas/normas , Técnicas de Diagnóstico Molecular/normas , Infecciones por Mycobacterium no Tuberculosas/microbiología , Micobacterias no Tuberculosas/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Análisis de Secuencia de ADN , Esputo/microbiología , Factores de Tiempo , Tuberculosis/diagnóstico , Tuberculosis/microbiologíaRESUMEN
Detection of heteroresistance of Mycobacterium tuberculosis remains challenging using current genotypic drug susceptibility testing methods. Here, we described a melting curve analysis-based approach, termed DeepMelt, that can detect less-abundant mutants through selective clamping of the wild type in mixed populations. The singleplex DeepMelt assay detected 0.01% katG S315T in 105M. tuberculosis genomes/µl. The multiplex DeepMelt TB/INH detected 1% of mutant species in the four loci associated with isoniazid resistance in 104M. tuberculosis genomes/µl. The DeepMelt TB/INH assay was tested on a panel of DNA extracted from 602 precharacterized clinical isolates. Using the 1% proportion method as the gold standard, the sensitivity was found to be increased from 93.6% (176/188, 95% confidence interval [CI] = 89.2 to 96.3%) to 95.7% (180/188, 95% CI = 91.8 to 97.8%) compared to the MeltPro TB/INH assay. Further evaluation of 109 smear-positive sputum specimens increased the sensitivity from 83.3% (20/24, 95% CI = 64.2 to 93.3%) to 91.7% (22/24, 95% CI = 74.2 to 97.7%). In both cases, the specificity remained nearly unchanged. All heteroresistant samples newly identified by the DeepMelt TB/INH assay were confirmed by DNA sequencing and even partially by digital PCR. The DeepMelt assay may fill the gap between current genotypic and phenotypic drug susceptibility testing for detecting drug-resistant tuberculosis patients.